This is a proposal for a K24 Mid-career award in Patient-oriented research (POR) for Kieren A. Marr MD, of the Johns Hopkins University (JHU) School of Medicine. Dr. Marr recently became the Director of the Transplant and Oncology Infectious Diseases Program in the Division of Infectious Diseases at JHU. The award supports the large goal of enabling leadership of this newly developed academic Transplant and Oncology ID program, with immediate goals of building an infrastructure to allow for structured teaching and research on infectious complications and initiating new directions of institutional research. The principal aims are to: 1. Develop a comprehensive academic training program for clinical and translational research in Transplant and Oncology Infectious Diseases; and 2. Define trends in epidemiology and ID outcomes by performing a prospectively maintained dynamic cohort study and building a database that combines elements from transplant and oncology databases, infection control records, and electronic medical records. As part of aim 2, new projects will be established to define the epidemiology and outcomes of Clostridium difficile infection in oncology patients, and to define infectious complications in high-risk recipients of solid organ transplants. These aims will be addressed in the context of providing mentorship to new and existing junior faculty, and to fellows and graduate students. The K24 will allow for Dr. Marr to more effectively pursue her long-term career goals of developing a world-class academic program at Johns Hopkins that specializes in the unique ID care of transplant and oncology patients, and building a multidisciplinary translational clinical research program focused on prevention and treatment of opportunistic infections.